The present invention relates to an improved bicycle pedal crank axle, and more particularly to a bicycle pedal crank axle including an engaging and disengaging gear that enables the axle and pedals connected thereto to keep unmoved while a chain wheel of the bicycle is caused to rotate reversely.
FIG. 1 schematically shows a bicycle and transmission gearing thereof. Typically, the transmission gearing of a bicycle include a pedal crank axle 11 pivotally connected to a five-way tube 1 on a frame of the bicycle, a large chain wheel 12 fixedly connected to the crank axle 11, two pedals 13 connected to free ends of two cranks extended from two ends of the crank axle 11, a small chain wheel 16 provided on a hub of a rear wheel 15 of the bicycle, and a chain 14 wound around the large and the small chain wheels 12, 16. When the two pedals 13 are alternately stepped, the crank axle 11 and the large chain wheel 12 fixed thereto are caused to rotate at the same time. The rotating large chain wheel 12 and the chain 14 together bring the small chain wheel 16 to rotate and thereby causes the rear wheel 15 to rotate forward. There are means provided between the small chain wheel 16 and the hub of the rear wheel 15 for the rear wheel 15 to keep rotating forward and the small chain wheel 16 to temporarily disengage from the rear wheel hub when the bicycle moves forward with the pedals 13 in a static state. However, when the bicycle is moved backward, the rear wheel 15 brings the small chain wheel 16 to reverse and the reversing small chain wheel 16 together with the chain 14 bring the large chain wheel 12 and accordingly the crank axle 11 to reverse at the same time. At this point, the pedals 13 are also moved reversely.
Reversing pedals 13 of a backward moved bicycle might cause little or even no trouble to general bicyclists, but they do bring considerable inconvenience to performers who play cycle tricks. The reversing pedals 13 tend to strike against or even dangerously stumble the cycle trick performers.
It is therefore tried by the inventor to develop an improved bicycle pedal crank axle to eliminate drawbacks existing in the conventional bicycle pedal crank axles.